Entered UK 1 day BEFORE Work Permit valid from date

I have a valid, stamped UK Work Permit valid from 16/10/06 and am now applying for ILR. However I entered UK on the 15/10/06 (I had previously been on a Working Holiday visa and left the UK then returned) and this is stamped on my Work Permit page. I have traveled many times since and my Work Permit is valid and has never been questioned.

When I rang to book an appointment I was told that having the stamped entry date one day prior to start of my Work Permit was highly unusual and that it didn't seem to be correct. I am now worried this endangers my application for ILR, even though the Work Permit is stamped and has to date seemed perfectly valid.

Any advice?

did u have a valid visa when u entered on 15th i.e, was ur working holiday visa valid on that date?