Can speakers sound worse during break-in period?

I purchased a NOS pr of speakers ( I’m not disclosing their name. Not interested in hearing from their haters) and was really liking them before I started to seriously break them in. It seems like after 24 hours they seem to have changed and sound worse, or not as good as they did. Are they just going through changes with some drivers opening up faster than the others? I know there are many components involved in this process and some might be a head of the others. I’m assuming that’s the case and when everything comes together they will sing.
NOS would suggest that your speakers are older (vintage) but never used. Do you mean to say never used speakers that were made in the last few years?
There not Vintage one generation back. They’re a pr the company never sold and offered them to a dealer at a special discount. 
It's been my experience different brands break in at different rates - simply depending on the materials involved. Revel says no break in time required, Buchardt at least 100 hours.
My Thiels probably took 2-3 months to break in, and it was quite noticeable when they did. Bass isn't something you imagine. The midrange also lost some forwardness/harshness, and people who'd heard early then later concurred. However my Maggies sounded great from the start and changed very little other than a bit more slam. Think ribbons are good to go out of the box.

I'd imagine different drivers are going to go through changes at different rates, so yes I can believe it could sound worse for a bit until they all get in sync. What I plan to do when I get my next set is simply put on the Stereophile test CD, and run it 24/7, louder when I leave the house.
"break in cant be measured its not real"
This statement is a load of crap.  I've been breaking in 4  - 15 inch woofers for about a week.  During that week,  FS has dropped around 3hz, QTS has dropped about .5 which is sizable. Not sure why someone would make such a statement, many other changes,  but break in is clearly measurable and over this time drivers,  all size drivers will make very noticeable changes. Normally the biggest change comes at around 4 hours of running them at decent levels,  it changes little by little until you hear real differences again at around 50 hours and still change on most drivers through 100 hours and I've seen a few speaker take even more.