Am wondering where you get your trust in the manufacturers? Over the last ten years we in the UK have seen some improvements in the Patient Information Leaflets that accompany our thyroid hormone medicines. They are slightly better at informing about taking with water and at least a bit away from food, have a much more comprehensive list of medicines that interfere, etc. But they still do not acknowledge things like taking at bed-time and miss numerous effects of others substances.
I have seen someone take T4 or, later, T3, and have visible effects within five minutes. This happened on many occasions.
If anyone suggests it is unusual, well, I am not in a position to judge.
At the same time, I am not convinced that so-called sublingual approaches are equivalent to swallowing.