I don’t know why Freedom passes don’t join journeys together with OSIs. I presume it’s to do with everything being free and perhaps wanting a simpler journey history interface on the photocard site. It’s the same with 60+ Oysters as well. I’m not aware that any checking of journey history goes on with freedom passes. If you were caught between Enfield Lock and Cheshunt then it would be a penalty fare. I guess they could look further into a persons history to see if it was a regular thing, but at the end of the day the pass isn’t valid that way and if you abuse it then you deserve what you get. I wouldn’t risk it myself.
As for Gatwick, you are following the rules if you touch in at the start and out at the end of your journey and stay within the Oyster PAYG area. If you were using PAYG throughout then you’d almost certainly exceed the time allowed for the journey. If you genuinely haven’t left railway premises throughout then you probably are legal, but if checked on a London bound train after leaving Gatwick then I would probably expect some questions.
I’ll send you an email in a minute because I’m genuinely interested in any information you have about the RID devices.