Cross Reference in SO

Hello,

X Item have following set up in F4104 - Cross ref table

X is linked with A - Cross Ref type = MR

X is linked with B - cross ref type = S

When SO is entered for X - it does not identify Substitutes exist, neither it shows green check mark.

This work for Item Y which have substitute as Z - and do not have any record for "MR" in F4104.

I have checked dates in P4104, Check box for Customer in billing page

Any clue why it work for one item which have only substitute record and does not work for other which have both S and MR ?