Excellent point otherwise, but...
Fortunately (or unfortunately?) that's not how the Couples Match ROL works...unless you put your prelim programs as your "Main Match" and the anesthesia programs as the "Supplemental Match" (which would be crazy).
When you and your partner both match at a given slot on your ROL, your supplemental list for that slot is "triggered." Whether or not you match in that prelim has no affect on your main match result.
That's why on the Monday of Match Week they tell you if you matched your main, supplemental, neither, or both, because any of the combinations is possible. If your supplemental match list ends up being too short, you'd have to scramble.
I am pretty sure you have looked at how the couples match works. Way more complictated then your triggered analogy. I should know, only took me about a month with 2 calls into the NRMP for me to get it. Your ROL gets crazy and you end up ranking programs multiple times, for example:
You and your S.O. like Denver. She does medicine and you do anesthesia.
That means you have 1 gas progam and she will end up ranking 2 medicine programs, but you will also be ranking 3 prelim programs. This is what your ROL will look like:
1 Wife CU med.......You CU anes.....prelim St Joe
2.Wife CU med.......You CU anes....prelim CU med
3Wife CU med........ You CU anes....prelim PSL TY
4 Wife StJoe med...You CU anes.....prelim St Joe
5Wife St joe med.....you CU anes....prelim CU med
6Wife St Joe med... You CU anes.....prelim SPL TY
7Wife CU med.....You CU anes.....(scramble/no prelim)
8Wife ST joe med...you CU anes...(scramble/no prelim)
9Wife CU med......you no match (scramble)
10Wife St Joe med...you no match (scramble)
11Wife no match(scramble)....You CU anes
So you can see how big a ROL can be and how you can rank a program multiple times. They (main and supplemental lists) are tied together. Like I said I did this last year and it wasnt a ton of fun. Hope this helps.