I know they are thawed by the fact that when I vigorously palpate them I do not feel any "cold spots". I feed prey straight out of the bucket, I do not have any substrate ingestion issues. I usually feed smaller prey items first as they get thawed in about 5 minutes (I use a good size bucket with plenty of hot water for volume heating), sanitize tongs, move on, then just rinse and repeat.
Can you describe in greater detail about how to palpate the specimens? I'm concerned my python regius specimens might be getting still partially frozen prey specimens or cold in the center specimens.