Yes, 1620 addition and subtraction do stop if the addend is shorter than the augend and
there's no further carry.
There was no pre-defined limit to the length of integer operands. If you had the memory to
do it, you could add two 10,000-digit operands. Floating-point numbers were limited to 99
digit mantissas, however.
On 1620 Monitor I, the default FANDK option was 4-digit integers and 8-digit
floating-point mantissas.