Sounds like a reasonable assessment. If a Stag-15 receiver is legal in CA then there should be no problem if a CA-FL resident transports one into the CA. I do not know when Stags were first produced so I cannot say if EVERYBODY bought one before the CA deadline. I can say that most California residents bought them in California. You, having dual state residency, are in a unique position.
My point with going through CA FFL is that removes any doubt as to when and where you acquired them. Your transaction is just one of the many thousands of lowers that were DROS'd in the last month. Also, in my opinion, there is less of chance that your AW registration will raise a red-flag if it shows a recent date of acquisition from a CA FFL. That's just my opinion. If you feel comfortable telling them you acquired it outside of the state, by all means, do so. Again, it's just my opinion.