Imperishable Night development picture has Letty Whiterock as placeholder
On 26th January 2004, ZUN posted on his old diary, a picture from the development of Imperishable Night. The page is now defunct, but it has been archived: web.archive.org/web/20040603101635/http://www16.big.or.jp/~zun/cgi-bin/diary/nicky.cgi?page=2
The image depicts Marisa Kirisame using her Master Spark bomb.
However, if you compare it with ver0.01, there are some notable differences. The name shown in the top left corner does not match the style and it looks like it says "Letty Whiterock", an enemy from Perfect Cherry Blossom not Imperishable Night.
The time points value is 1000, which not even on Easy mode of ver0.01 is that low. The difficulty does not appear on the HUD and also the numbers you see on top of the screen seem to be debug mode values. There are some other minor differences such as the text padding in the HUD and the "Enemy" indicator looking slightly different.
If you compare this picture with Perfect Cherry Blossom, you can clearly see it says "Letty Whiterock". The font, the size, the colours match perfectly to it. Also it seems that the "Enemy" indicator in this development picture is from Perfect Cherry Blossom as well.
Curiously enough, if you rip the files from ver0.01, the enemy list includes few Perfect Cherry Blossom characters, which were later removed from the ver0.02 files. Even so, Letty Whiterock is not present on it, the names start only from Lily White.