BIOS updates usually only write to certain regions, and does not always erase then write, unless programmed to do that which is not always the case. Sometimes only update if new/different data within a region by the byte. So, sometimes any microcodes that are there for example, that aren't in the BIOS you are flashing will remain, unless it erases then writes. Sometimes BIOS updates are set to only flash certain regions too, so microcode may be one that is passed over by the stock flasher, especially if they over several updates never added any then it may be a block they don't include in the normal flash command switches. It really all depends on the flashing program and how it flashes, and the commands /flags used during the update too.
For your peace of mind, I can show you BIOS micrcodes/dates/versions included before and after I updated those, if I didn't already include that image in the BIOS package when I uploaded it for you (I usually do). The microcode was always there, it just wasn't up to date to the latest possible version, that's why I updated it.
Here's an image showing the microcodes included in the two files you attached
And here's the one comparing stock mod BIOS vs the one with updated microcodes I sent you before, looks like same comparison
On the BIOS image, it could be any number of formats, does not necessarily have to be a BMP.
PNG, JPG/Exif, BMP, EPA, GIF, PCX, TGA, TIFF, ICO, WMF, J2K, JXR, WebP, JP2 (JPEG 2000 Image Format (*.JP2, *.JPA, *.JPM, *.JPX))
More common image formats used back then for logo's/splash images would be BMP (but actually AWBM not real BMP), EPA, TIFF, TGA, or PCX
You'd have to lookup hex headers or markers for each to maybe easily find them.
When looking for images in BIOS, here's the some headers / signatures for some image formats
42 4d (4D42) is BMP \x42\x4D
Others are more complicated, but you can look them up for an easier summary. Just look for each type of file in google and it's hex header or signature hex
Here's some I pulled from a UEFIImage extractor's python file.
BMP
(\x42\x4D.{4}\x00{4}.{4}\x28\x00\x00\x00')
PNG
(\x89\x50\x4E\x47\x0D\x0A\x1A\x0A')
(\x49\x45\x4E\x44\xAE\x42\x60\x82')
JPG (Starts with FF D8 FF. Ends with FF D9
(\xFF\xD8\xFF\xE0.{2}\x4A\x46\x49\x46\x00) # JFIF marker
(\xFF\xD8\xFF') # Any marker
(\xFF\xD9')
GIF - GIF8 (GIF8) (hex: 47 49 46 38), followed the version 9a (hex: 39 61)
(\x47\x49\x46\x38(\x37\x61|\x39\x61)')
PCX
(\x0A((((\x00|\x02)|\x03)|\x04)|\x05)\x01(((\x01|\x02)|\x04)|\x08).{60}\x00(((\x01|\x02)|\x03)|\x04).{2}((\x00|\x01)|\x02)\x00.{4}\x00{54})
TGA
(\x00|\x01)(((((\x01|\x02)|\x03)|\x09)|\x0A)|\x0B).{4}((((\x0F|\x10)|\x18)|\x20)|\x00).{8}(((((\x00|\x01)|\x08)|\x10)|\x18)|\x20))
TGA2
(\x54\x52\x55\x45\x56\x49\x53\x49\x4F\x4E\x2D\x58\x46\x49\x4C\x45\x2E\x00.')
TIFF
(\x4D\x4D\x00\x2A|\x49\x49\x2A\x00)')
Purchase a programmer and SOIC8 cable, they may not be needed for this system, but you'll be happy you have them some day in the future
Plus they're so cheap everyone should have a set. What kind of BIOS chip is in this system anyway, you may not even be able to use common cheap programmers that are around today, you might need special $16-20 one if it's PLLC32 BIOS