I'd tend to agree with GM. 1724382 & 1721704 on both of those with the 9 added sometime before import is what my vote would be.
There is unfortunately very little information on this arsenal and few examples are documented. We don't even have any year 17 examples for them, so we have to go off what we do know.
There is a year 15 gun from this arsenal that is 151666X serial number:

While I can't really make out the last number, it's clear that this gun is after #16,660 in this series. Year 17, two years down the road could easily have had an additional 8k guns made, so the 24k guns isn't out of the realm of possibility even though many other years appear to have been very low production.
One of the reasons I think the 9 was added later is the spacing between the 五六式 and the S/N. Look at these examples and then look at the OP photos:







There is a good even spacing there even though the year 20+ guns that spacing decreases a bit. The OP photos look squished together badly, remove the 9 and they would look the same as those above.