Healing and moon-duration

Yesterday evening we came up with a little problem. If you have an Heavy wound, it is not possible to help the person with Purification of the festering wound. The spell must cover at the entire time of recovery, and after the spell is cast the recovery sets back to 0. This gives problems because the spell has a duration of moon, and the healing time of such a wound is much longer.
How do other people handle this problem, just accept the fact that casting such a spell when having a heavy wound is useless? Or do you house-rule this otherwise?

By casting spells that overlap each other in time

the spell description states that the recovery time is set back after casting, so after you cast the second spell the whole process should start all over again. We plan to house-rule that overlapping spells do not pose any problem, but I was wondering how other people interpreted the rules.

Never noticed this before. I doubt that the purpose of this statement was to prevent multiple castings. I suspect that it is just sloppy wording meant only to clean up ambiguity caused by a recovery period that is split up between two separate recover bonuses. (which is used? do you make a time weighted average?).

I'll house rule it in exactly the same way that you suggest.

It was confirmed (possibly by the line editor, I can't remember) that the intent is indeed that you can cast such spells multiple times while the patient is recovering. Healing doesn't start up from scratch every time - unless you give up on magical healing or were using temporary "heal an X wound" spells.