ID these DEC floppy disks

[Chris Zach]

Hey all!

While going through floppies I found these and was wondering what they 
were. Only clue in Google was someone asking in 1997 same thing.

BL-T540B-M1 CZUFDB1 USER TESTS
BL-T541B-M1 CZXD1B1 FIELD SERVICE TESTS 1
BL-T542B-MC CZXD2B0 FIELD SERVICE TESTS 2
BL-T565B-MC CZXD3B0 FIELD SERVICE TESTS 3
BL-T583B-MC CZXD4B0 FIELD SERVICE TESTS 4

Any ideas? The first one does not have a write protect tab, the others 
do. There is also one other disk I found

CZMX4E0 Micro 11 Maint RX50 4

On this one the write protect flag was torn off (was on from factory and 
removed)

C