Here is the thing. No blade "needs" sealing. Sealing is a choice. Some blades with delicate top plies benefit from sealing. Some blades, particularly certain blades from Stiga, are made in a way that makes it very easy to splinter the top ply. Sealing would be beneficial to the top ply of those blades. Please note: I did not say "need"; some blades would benefit from being sealed.
Some people like to seal all blades. Some people do not like to seal at all for any blade.
A strong wood like Koto probably would not see much benefit from sealing (maybe only a little but not a lot).
Blades with very good build quality like Butterfly blades usually don't benefit that much from sealing.
However, here is the thing about water and wood.
If you take a piece of wood, any wood, any kind (but not sealed) and every ten or so days you pour water on it and let it dry, the water will sink in. Then the water will evaporate and be gone. Now, if you did this just once, it would do a little but not much. But done consistently, over time, it would have an impact on the wood. The water causes the wood to expand and then when it evaporates out of the wood, the wood contracts. The water would cause the plies that had more water to expand more--the top ply would absorb more water from the glue than any other ply. Over time this causes the wood to warp.
I would be willing to bet that a lot of guys who have old blades that are not sealed, if they took their rubbers off and placed them on a flat surface, there would be a certain amount of warping to the wood of the blade so it was not flat. That will impact the blade's performance.
Over time the water sinking into the wood and then evaporating out of the wood, will also cause the wood to have a duller feel. Sometimes that may be wanted and sometimes that may not be wanted. Each person will experience that differently. But over time, that will make the blade slower. Again for one person that may be just what was wanted. And for another that may be the opposite.
Now the reason I said 10 days is, that is about how long many top pros use a rubber before changing (sometimes it is one week, sometimes it is two). So, what I have explained, means that for a pro, after about a year, the performance of their main blade will be diminished enough that they may want a new version of the same blade.
For a normal player, it may take 4-8 years before the blade's performance was changed significantly enough to cause them to want a new blade. And for someone who was using a blade that was initially too crisp or too fast, the water damage that occurs may simply make the blade better for that player.
But sealing would protect the wood a little from the consistent water damage that will happen every time you use a water based glue on your blade.
As far as needing to reseal, if you did the job right the first time, you should never need to do it again. The wood of a patio deck at a beach town resort may need to be finished once a year as the deck is exposed to heat, cold, rain, sea salt over and over. But if you seal your blade with a thin layer of sealant, it should never need more than that unless you use a solvent to remove the sealant.
As far as chips and dings on the edge of your blade: don't worry about them. You don't hit with that part of the blade. If you wanted to put sealant on that part you could. It wouldn't really hold it together though. It would just protect the wood fragments from water damage. Wood that is already damaged is not held together by a sealant. Wood that is not damaged can be protected, in part because the sealant makes it easier to remove the rubber. Too thick a layer of sealant would not be good either because it would impact the way the blade performs.
With the issue of the edge of your blade, one thing to remember is: you usually are trying to hit the ball with some area in the center of the racket. When you hit the edge or, even, within 5mm of the edge, it is usually a mishit and if it does go on the table, an accident and a poor quality shot.