Welfare wise, there's not an issue.
As you're doing some soul-searching next week, I will comment on this.
I wonder if you are a little bit in denial... If you have to book time to do whole-flock treatments 'months and months in advance', then you cannot react quickly if something unexpected happens (and also must be using prophylactic treatments or you would be getting the unscheduled need for treatment.)
My own wee fleece flock is very happy where I am keeping them, but I have no handling pens there and it takes some organising and help to get them back to the farmstead for treatments. Fitting their needs in around the 'proper sheep' and cattle sometimes means that I am not getting my hands on them quite as promptly as I might like. I'd never let them suffer, of course, but I know, deep down, that they wait longer for treatment sometimes than I would like.
And compromises have to be made. Some of the boys got burdizzoed this year as I wasn't able to get them in to catch the lambs that were too small to ring when I could catch them in the field
. (Actually, the burdizzoing went fine, so I will be happy to do that again. We burdizzo the bullocks, so BH knows exactly what he's doing.) I've been watching a few girls with daggy backends like a hawk in case they got strucken before clipping. (They didn't, this year - too cold for flies, mostly.) I won't bring in any more longwools for this reason (but will breed more longwool x Shetland, they seem to manage better on the whole. I'll cull / not breed from any crosess that get mucky.) I hand-reared a lamb which was rejecting its (first-time) mother, because on that day with that sheep, I wasn't able to bring the family in for bonding. Indi is fine, a lovely lamb doing really well, and her mum is making a great job of her sister - but Indi would've done better on her own mother, if I could have managed it.
So no-one comes to any
harm, but I know in my heart of hearts that I can't always do things as well as I would
like. And I suspect, that in your heart of hearts, you may feel the same.
I've got a very low stocking density down there, so they are managing very well with few treatments so far. But I do need to take care to not let the numbers increase to a point where the worms and fluke build up... (We do graze with cattle when we can, but can't always do that as much as we'd like, if the river is very low or the ground is too muddy...)
So I am rigorous on culling sheep that have bad feet, seem to keep getting worms / mucky backsides, and so on, to reduce the incidence of needing to bring them in.
Now I know that my sheep live the life of Riley and are very happy. But even so, those days when I know I have some wormy backsides I can't yet dose, some boys getting larger and not yet burdizzoed, there is a niggling little stress inside somewhere...