Your assembler probably requires that numeric values must begin with a digit - otherwise how could it tell if, for example, "DEAD" was was supposed to be a hex number (0xDEAD in 'C' notation) or a variable called "DEAD"?!

Therefore, if the most-significant digit of a hex number is >9, you have to add a leading zero to meet the "must begin with a digit" rule.

However, adding leading zeros makes no difference whatsoever to the value of the number - so it makes no difference at all if you add more than one!

One reason for having the extra zero in your example might be for consistency - so that all hex numbers are always written with 3 digits, the first always being a zero.

Warning:
Be careful with this in 'C' - by default, 'C' assumes that any number beginning with a zero is Octal

000 = zero
001 = one
002 = two
003 = three
 :    :
010 = eight!!!

Of course, the 'x' in the 'C' 0x... notation distinguishes a hex number