Hard to know....
Before the new BRP roll out, they would usually ignore the intended travel date and issue the visa from the date they approved the application.
But they seem to be paying attention to travel dates now (obviously a good thing).
As your application has been sitting there for so long, I cannot imagine you will have an issue. I would anticipate they will make the visa date valid from the date you requested.
Had they looked at the application asap, they could have refused the application (though I think highly unlikely. I think they would have just issued it as valid from that day and left you to "deal with it.").