Is this normal?
I've had about 5 days worth of printing on the core one. Mostly satin sheet. I made sure sheets are dry before I put them in. I have a MK3S+ with about 30 days of print time on it and that bed doesn't look like this. This bed still heats up fine and prints are still good though.
RE: Is this normal?
Try to clean it with IPA, the base plate shows super easily any grease stains (from fingers for example).
Nothing to worry about!
RE:
Mine does look somewhat like yours. I usually clean it with IPA.
What seem to happen from the surface appearance on the edges and the middle is my finger grease pattern. When I remove a print sheet with a sample still attached to it I usually pick it up by the edges and apply some finger pressure near the middle to bend the plate. If the sample is well attached I'll do the same at 90 degrees. I then put the sheet back on the heating surface.
The shiny pattern on the heating surface does correspond well with my touch points on the back of the build sheet.
REPAIR, RENEW, REUSE, RECYCLE, REBUILD, REDUCE, RECOVER, REPURPOSE, RESTORE
RE: Is this normal?
Yep, normal! The LEDs are absolutely brutal regarding this. My Satin sheet looks "nasty" just by looking at it in a wrong angle and the heatbed looks greasy as soon as you breath too close next to the printer.
You can get rid of most spots by using IPA, but it doesn't really matter and is basically just a visual thing.