Does anyone understand the 2450S and 2451S differences?

The 2450H and 2450J are both 2" drivers. 8 and 16 ohm respectively.
Similarly the 2451H and 2451J are both 1.5" drivers in 8 and 16 ohm.
The two H's uses the same repair kit and similarly the two J's.
I.e Just the exit body differs.

I believed the 'S' models were a later version with a non ribbed and Aquaplas dusted dome/dia.
So I assumed the model names would follow the same pattern.

Not true! - In fact the 2450SL is actually a 1.5" driver with a unique repair kit in 8 ohm only.
The 2451SLJ has a unique repair kit in 16 ohm only.

Is this just an inconsistent nomenclature issue?
I.e. The consistent name for the 2450SL would be 2451SLH ?
Or is there some other difference in the driver that makes sense to call it a 2450 rather than a 2451?

As a DMS-1 wannahave I wanna know!