LM1558: Date code clarification

Part Number: LM1558

We need how to read date code =  +5 indicates what.???

CD4011BM- Date  code-  1631+5

CD4001BM- date code-  2322+5 

CD4012BM96-Date code- 2346+5

CD4049UBD- Date code 1614+5

LM1558H- Date code 1727+5

COCHRM260170(R26002617).pdf