Bob, I have been able to get some further info over the past 2 years. So far I have 4 different date code systems, 3 on hoses and 1 on ferrules (at either end of a hose assy).
Here goes
Therapy Key
A B C D E F G H I J
1 2 3 4 5 6 7 8 9 0
Format AAF/JI where first letter is year (ie A-2001)
Datex Ohmeda Key
B R I T O X Y G E N
1 2 3 4 5 6 7 8 9 0
Format NY NI NN where last two letters is year (ie NN-2000)
Oxylitre
OX (x inside the o) marked on ferrule with 2 digit number corresponding to year
MIE/Intersurgical Key
As Therapy code
MEC Key
S V H Y F L O M E D
0 1 2 3 4 5 6 7 8 9
Format YSS/FSV where last letter corresponds to year (ie v-2001)
Hope this is of use, and I must apologize if there are any errors.