I have had similar experiences trying to pull down the installed jumbos and have had success with using this OID:
1.3.6.1.4.1.2620.1.6.20.7.1.2
In our monitoring system, I have made some customer poller that has helped a lot with reporting/inventory.
Vendor: 1.3.6.1.4.1.2620.1.6.16.9
Machine Type: 1.3.6.1.4.1.2620.1.6.16.7
Software Version: 1.3.6.1.4.1.2620.1.6.4.1 <=This gets your main train version (R81.10 for example)
Software image: 1.3.6.1.4.1.2620.1.6.20.7.1.2 <=This gets the name of the Jumbo hotfix file ( "Check_Point_R81_10_JUMBO_HF_MAIN_Bundle_T170_FULL.tgz" for example)