Digital BW, The Print

I enlarged a whole portfolio in Brightcube semi-matte paper ,VM Inks,sprayed
with Krylon 1305. It gave beautiful results. Then,after presenting it,the
albm stayed closed for about 45 days. Today I opened it,and to my
surprise,the following happened:
1.Prints got posterized in the shadows,which they were NOT before.
2.Some of the bronzing came back,now with a yellowish cast...


Any ideas why that can be???

Andr\ufffd