Once you get the terms and conditions, they are somewhat more specific (I have them in my hand).
You are not required to have completed an offshore passage, you are required to have completed a 250nm cruise. It doesn't need to be offshore. You'll probably rack up those miles in the coastal trip to get to Portsmouth, VA.
The ISAF is a red herring. Any captain is going to make sure they have the appropriate safety equipment.
The inspection is also a red herring, it doesn't always even happen (two different captain's experiences):
"However, we are told that this year, we are to inspect our own vessels and have our crew sign the safety inspection. I am extremely disappointed with this last minute change ... This is one of the touted benefits of rally participation that I signed up for and it is just done away with without any explanation! I know that other captains were looking forward to this as was I, not only to have three other trained eyes looking over our preparations, but to learn from one another different and possibly better ways of making our boats safe and ready for ocean passages. But my crew and I go through the safety checklist checking each and every item before signing it and turning it in."
The event organizers had distributed a "required equipment list" and all boats were expected to have the items. Compliance was checked during the safety inspections, but not necessarily rigorously. For example, we said our compass had been adjusted and had a deviation table, but we didn't have to show the deviation table (which didn't actually exist).
The bottom line is both are a bunch of boats heading off for a long passage, and both using virtually identical weather services. Arguably, there is more offshore experience associated with the crews of the SDR than the Carib 1500.