Planning expert to give view on 4 year rule please

Hi there. Was wondering if there are any planning experts/lawyers on here who could give me a 2nd opinion please. I have a property which is divided into self contained studios, but I can find no evidence of planning permission.

They have been in existence for just over 4 years (which I know is significant) but I got them 18 months ago. Apart from one studio, the others have been empty, because as people moved out, I did not replace them as I was a bit scared to do so in case as the property was going through probate. However, all of them were rented out for the first 2 years continuously on ASTs.

I had read that in order to apply for a Certificate of Lawfulness (which means if things have been existence for 4 years or more you can apply for them to be legal), the 4 years have to be continuous. A planning lawyer who I consulted said that he would argue that the layout and alterations have themselves been in existence for 4 years so the fact that they haven’t always been tenanted would not be the test.

I was hoping to get a 2nd opinion from those qualified to answer on this last matter.

Thank you

Sharron