Here’s the schematic by Rene Schmitz that the LMNC Performance Filter is based on. (Not sure if that’s the filter you’re building though, but if not, similar ideas apply.)
The control current is supplied by one of the transistors via two 10k resistors, one on each side. For the LM13700 (used instead of the even more obsolete CA3080) these resistors connect to the control current inputs, pins 1 and 16. In the worst case scenario the transistor output is 12 V. To avoid blowing up the LM13700 the control current must be below 2 mA. By Ohm’s Law the worst case is I = 12 V / 10k = 1.2 mA. So as long as those two resistors are really 10k, and there isn’t some short or other such problem, and there isn’t a 20 V voltage around that can somehow get onto those resistors, a genuine LM13700 will be safe.
There’s some discussion of this stuff here:
https://electricdruid.net/design-a-eurorack-vintage-vca-with-the-lm13700/
which is about designing a VCA, not a VCF, but as far as control current goes it’s a similar thing.
The letter suffix just indicates the package: M or MX for surface mount (SOIC), N for through hole (PDIP). So what you have is what you want — or at least it’s marked as what you want.
Unfortunately there are few reliable (non eBay, non AliExpress, etc.) mail suppliers, if any, that still sell the through hole LM13700. Pretty much any mail vendor that claims to have them might be selling legit new old stock, maybe used chips, maybe no-name copies, maybe downright counterfeits, and it’s near impossible to know until you buy some and test them. At this point buying the SOIC version and an adapter board as described above is probably your best bet, unless you’re fortunate enough to have a reliable local electronics parts store that maybe still has a box of them.