I strongly disagree. That requirement is vague and can be interpreted in multiple ways. For the two store ops, the requirement to be within dynamic memory indicates a possible error condition. But when that is triggered will be different depending on how you interpret the signedness of the operands, handle overflow, and with what bit precision your arithmetic is done in. For the other two ops, the requirement to stay within dynamic and static memory can still be smaller than 64K if the story file is also and suffers from the same problems as above.
Explicitly saying all math operations in those ops must be wrapped modulo 16-bit and the final result interpreted as unsigned before checking against the limits of dynamic memory or the story file removes any ambiguity and makes whether or not the operands are signed or unsigned completely moot.