No Expert but I do know a little about dice. The cracking and general decomposition is From the decaying of the Cellulose-nitrate. An unstable material if not originally cured properly - and then sometimes not even then. DO NOT EXPOSE THESE TO DIRECT SUNLIGHT - LIKE ON A WINDOW SILL -THEY CAN IGNITE WITH HEAT - DO NOT BURN CELLULOSE NITRATE (GOOGLE). Better kept in a cooler temperature or they will off-gas the vapors. I would not put them in an airtight box as they will off-gas and the cube will cook in its own gasses and ultimately denigrate.

Bet you are really excited about them now - but very collectible - in spite of their problems. Looks like an early Mason style.

As for the spots - called "TOPS" or mis-spots - this die can be mated to another mis-spotted die with only odd numbers - impossible to throw anything but an odd number. Different combinations of mis-spotting result in better or worse possibilities for some numbers. They can be used by a "flat" house or run in by a player - yes even with a logo that is close to an original. If the house was cheating, then correct logo. Check a KC Card catalog to further your education.