There will be IMSI Analysis Table where IMSI Format ( E212 ) will be transformed to E214 Format,which will be used for Routing the message to HPLMN.
E212 IMSI – MCC+MNC Will be Replaced By
E164 – CC+NDC
Result = E214 = CC+NDC+Remaining Digits in IMSI.Called as MGT-Mobile Global Title.
In the MAP-UL Message this will be used as called address.In the same message Full IMSI will be there.Which will be read by HLR Properly.