Why is Woff file downloading instead of just Woff2? Google Fonts/NextJS

Question

NextJS has font-optimization for Google Fonts where it downloads the font-face definition from Google Fonts (with both a Chrome and an IE User Agent) and places this definition in the head of the DOM. This is to speed up the download of the required font.

When using a URL with individually specified weights such as https://fonts.googleapis.com/css2?family=Open+Sans:wght@300;400;700&display=swap, the font family definition for font-weight is a single number. E.G. 700. In a Vanilla NextJS 12 application using Chrome, this correctly downloads a single Woff2 file.

When using a URL with a range of specified weights such as https://fonts.googleapis.com/css2?family=Open+Sans:[email protected]&display=swap, the font family definition for font-weight has two numbers. E.G. 300 700. In a Vanilla NextJS 12 application using Chrome, this downloads a Woff2 file along with a Woff file for each font-weight.
If I edit the NextJS optimization script to avoid Next pre-downloading the font-definition using the IE User Agent.... I correctly only get a single Woff2 file downloaded.

Why? Is this a bug in Chrome? Or NextJS?

I am assuming that because the font-weight is specified with 2 numbers, Chrome is choosing the more precisely defined font-family that was defined from the IE User Agent and therefore downloading the Woff font. But if that is the case.... Why?

This is the resultant font-definitions:

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300;
    font-stretch: normal;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsiH0C4k.woff) format('woff')
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 400;
    font-stretch: normal;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsjZ0C4k.woff) format('woff')
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 500;
    font-stretch: normal;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsjr0C4k.woff) format('woff')
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 600;
    font-stretch: normal;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsgH1y4k.woff) format('woff')
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 700;
    font-stretch: normal;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsg-1y4k.woff) format('woff')
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTSKmu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+0460-052F, U+1C80-1C88, U+20B4, U+2DE0-2DFF, U+A640-A69F, U+FE2E-FE2F
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTSumu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTSOmu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+1F00-1FFF
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTSymu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+0370-03FF
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS2mu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+0590-05FF, U+200C-2010, U+20AA, U+25CC, U+FB1D-FB4F
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTSCmu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+0102-0103, U+0110-0111, U+0128-0129, U+0168-0169, U+01A0-01A1, U+01AF-01B0, U+1EA0-1EF9, U+20AB
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTSGmu0SC55K5gw.woff2) format('woff2');
    unicode-range: U+0100-024F, U+0259, U+1E00-1EFF, U+2020, U+20A0-20AB, U+20AD-20CF, U+2113, U+2C60-2C7F, U+A720-A7FF
}

@font-face {
    font-family: 'Open Sans';
    font-style: normal;
    font-weight: 300 700;
    font-stretch: 100%;
    font-display: swap;
    src: url(https://fonts.gstatic.com/s/opensans/v29/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2) format('woff2');
    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD
}