I have a daffodil patch that was planted 12 or so years ago. It has never been divided. The recent years are full of leaves and not much flower bloom. I would like to divide them so they are not crowded and hopefully more flower bloom. Can I dig them up and divide them in the next 2-3 weeks (early to late Oct) or should I wait until after the spring bloom? Every website I read seem to say late spring. I live in Philadelphia area. Thank you.

I do not have time most springs to get this chore done and
have found daffodils very forgiving I have often dug and divided in the fall.
The only real problem with fall, if you have squirrels is their curiosity, they often dig the bulbs up to see what you are burying
Consider adding a bit of bulb booster fertilizer when you replant and you will be rewarded.

When I replant bulbs, I prefer to wait until spring, when the foliage first starts emerging from the ground.
My reasoning is that when moved at that time, the plants go ahead and grow and look great.

If you wait until after the bloom, the plants just turn yellow, and you've got a long time to wait to see any benefit.

As far as trying to replant now... first you've got to find the dormant bulbs, and then you've got to try to dig them without injuring them... not so easy... and again... there's that long waiting period...

Daffodils MUST produce new roots in the fall to live the next spring. If you were planting dry, bought bulbs, it would be too late to plant if you are in zone 4. But since these daffs are already in the ground, then you can transplant/divide anytime in October. Summer into early fall would have been better, because, unlike then, now you need to be very careful not to break the new roots off. If you break them all off, most likely no more will grow and the bulbs will die next season.

I also vote try to do it now. You will have many many bulbs under there, so if you accidentally cut a few it's no big loss. You should be able to keep the best of them and have plenty to pick from, discard the smallest and any with damage.

Welcome to NGA, @HeyIngrid !

I agree with dividing and replanting them now; I think you have a better (although not guaranteed) chance of getting blooms next spring.