For a while, Graupner made an L version of its telemetry HoTT receivers (GR-16L, GR-24L, GR-32L) which had slightly different software with reduced functionality compared to the non-L receiver version. 

The hardware of both receiver models is 100% identical. 

The L receiver version is not manufactured anymore and is replaced by the standard version (GR-16, GR-24, GR-32). As of 2019, the L models' software limitations were lifted, bringing the L and none L software to the same software release base, making them 100% identical for both hardware and software. 

To ensure your L receiver version has the same software as the non-L version, you will need to update the software on your receiver with the latest software version. 

 GR-12L and GR-12

The primary differences between those two receiver models are the software. 

The GR-12 has additional curve mixers digital switches and supports serial outputs such as SUMI, SUMD, SBUS, SUMO, and SUMD3 support for the mz-32 to enable signal output above 16 channels. 

The GR-12L also provides support for SBUS, SUMD, SUMD3, and SP2048 serial protocols, and for those flying copters, you can designate the output channel of the RSSI signal for your flight controller. 

Fundamentally there are no differences between both receivers unless you need additional mixer functionality the GR-12 has. 

If you are looking for an all-rounder six-channel receiver with good range, telemetry, digital serial output at an affordable price, the GR-12L is the receiver to choose.