I'm not sure if you saw my recent experience with this (post # 7 on Can't apply tsu when using promo night and points night )

I had booked a multiple nights points reservation with a TSU applied and confirmed, and separately booked a free night reservation the night after that using my annual cat 1-7 free night. Months later, I emailed my concierge a list of approaching reservations to check that all my suite upgrades were properly applied (since they don't show up online for TSUs applied to point stays), and they said someone had removed my TSU from that particular reservation . When I asked why, they looked into it, and said it was against the terms of WOH to have a TSU applied to a reservation back to back with a cat1-4 or cat1-7 free night (even on separate reservations) and emailed me the section of the terms she said it violates. She did mention if I had booked the cat1-7 night as a GOH for my wife, it would be considered a separate stay and be ok, but some others on the thread I previously posted this raised the concern that doing that might be too obvious a workaround and raise the same concerns.