Is the Regular weight 390 or 420? (Typo in ReadMe.pdf?)

Page 10 of the [current `SourceHanSansReadMe.pdf`](https://github.com/adobe-fonts/source-han-sans/blob/a4f7cf94edfb9d7ffbdfc4841de276358bd7e0f2/SourceHanSansReadMe.pdf) provides the interpolation ratios of weights.
It says Regular is 420.

> **Weights**
>
> The table below shows sample glyphs in each of the seven weights, ranging from ExtraLight to Heavy. The ExtraLight and Heavy weights represent the master designs, and the five intermediate weights are the result of multiple master interpolation (the interpolation ratios are provided):
>
> ExtraLight—0 Light—160 Normal—320 Regular—420 Medium—560 Bold—780 Heavy—1000

However, in `Masters/designspaces/*.designspace`, the Regular weight is interpolated at 390.

https://github.com/adobe-fonts/source-han-sans/blob/0b993716f6910f0c8e00f957c767ab3cf5cb7602/Masters/designspaces/SourceHanSansSC-VF.designspace#L4-L12

Is this a mistake in the PDF? I guess the correct value should be 390, because Regular looks very similar to Normal (320), rather than the middle weight between Normal and Medium ((320 + 560) / 2 = 440 ≈ 420).

## Previous discussions in 2021

https://github.com/punchcutter, a member of https://github.com/adobe-fonts, said in https://github.com/adobe-fonts/source-han-sans/issues/297#issuecomment-819550592:

> There are only two masters and no intermediates. There is mapping, though.
> 0 -> 250
> 160 -> 300
> 320 -> 350
> 390 -> 400
> 560 -> 500
> 780 -> 700
> 1000 -> 900

Someone [asked later](https://github.com/adobe-fonts/source-han-sans/issues/297#issuecomment-924830191):
> would you please double check whether it's 390 for Regular? Per this [ReadMe](https://github.com/adobe-fonts/source-han-sans/blob/release/SourceHanSansReadMe.pdf?rgh-link-date=2021-09-22T11%3A12%3A46.000Z) file, it should be 420.
>
> Never mind, I saw the comments earlier from https://github.com/punchcutter.

https://github.com/punchcutter [replied](https://github.com/adobe-fonts/source-han-sans/issues/297#issuecomment-924835348):

> Ah, thanks for catching that. I need to update the PDF. The whole build process changed from when that was written, but I overlooked those values in the last PDF update.