You lose formatting when you concatenate so if, for example, A1 has the number 12 but is formatted to show 0012 then when you concatenate you lose the formatting, e.g. with "text" in B1
=A1&" "&B1 gives
12 text
If you want it to be 0012 text then use TEXT function in the concatenation, something like this
=TEXT(A1,"0000")&" "&B1