Exclude column from Data Validation

[ipbr21054]

Morning,
On my worksheet in 3 different columns i am seeing them circled as invalid.
Column B is a car registration & column J is a code & column L is a chassis number.

What i now find is that when i use "Data Validation Circle Invalid Data" i see a message to say that i have more than 255 items & only 255 items will be shown.

So basically im not seeing all the issues because of the data in column B,J & L eating up my allowed search results if you know what i mean.

To be honest i dont even see why they are even circled as invalid.
I have looked for a pattern with these and the other cells that pass ok but see nothing.

The only thing i can think of is the drop down option.
The option is N/A or i just type in the cell.
So by not selecting the option & typing something different,i thought this was the answer.
The reason why i now dismiss that is because in another cell the drop down option is also N/A but when i type a year say 2008 all is fine.

I say all is fine because it is not circled as invalid BUT is that because it is outside of my 255 allowance ?
I also can say the same for column A where i type a name,there is no drop down in this column and none are shown as invalid.

Im lost

Thanks