73H is code for the 737-800s that have been modified to have:

1) AVOD from nose-to-tail
2) 144 Y seats (instead of 134 on the "738") - new slimline seats; F remains at 16 seats
3) Winglets

On the occasion that people have been on a non-AVOD 738 when it was originally advertised as a 73H, it was due to an equipment switch (just like when a regular 757 subs for an ex-Song 757). But when a flight is designated as being operated by a 73H, it is indeed supposed to have nose-to-tail AVOD.

In this rollout period, there are bound to be instances of 738s substituting for 73H as IROPS could potentially screw up the rotations of the still-nascent 73H fleet.