Does over boosting remove the previous boosts?

Question

I've been playing with boosting Pokemon (baton pass/dragon dance, ect.) and in the longer battles, I've noticed that I either seem to lose speed over time or remove the speed boosts somehow. The main culprit is Dragonair. At +6 speed, it will be faster than a Pokemon I'm battling, but after a while I am no longer faster than the same Pokemon (who hasn't boosted speed in any way). I am using Rest/Sleep Talk and it occasionally uses another Dragon Dance prompting the "It's attack and Speed can't go any higher" message.
Does boosting when you're maxed out remove the previous boosts?

Comments

I couldnt answer your question thats why this is a comment but you might wanna try that on pokemon showdown.

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I highly doubt it would decrease if it got over-boosted.
They probably did use some Speed-increasing move, you just didn't notice.

Answer 1

No.

If you use a move that boosts a stat that is already at its max, the move will just fail and it will that that it can't go any higher.

If you lost the boosts, you either switched out or used a move that lowered your stats, or your opponent used a move that lowered your stats.

Here is a replay of me testing it on Showdown with myself.

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Source: knowledge and testing
Hope I helped.