In spite of the size of picture can't really trace the wires but it does seem that L1 and L2 are used in at least one of the three switches.
First definitions gang refers to number of switches is a block so you have a three gang switch. Way refers to the switching options so a rotary selector switch on your oven could have 7 ways but a standard switch can only have two ways or on/off you may get two way centre off.
So a switch with Com and L1 and L2 is a two way switch we also get a change over more commonly called a intermediate switch.
Two way refers to the two options and even if you have 6 switches to work the same light it's still two way.
So wire count I make to seven one I will assume is line in so 6 wires out. That would indicate all three switches are wired as two way. i.e. no terminals unused.
Since except for the line there seems to be only a single wire in each terminal my thoughts is this is the last switch rather than the first switch.
Looking as a standard wiring diagram it would seem the main of first switch has 5 wires per switch and the last one three wires per switch.
So it seems you must find the other switches. Lucky you have not plastered yet as it seems likely you will need to move some wires to get this switch to work a single light.
Even in my mothers house 1954 two way pull cords were used if that's the case then easy access but you need to find the other switch as likely that one is the master not the one you show.
The problem is permitted zones. So that people do not drill into cables we have rules as to where cables can be run. It is considered that a switch or socket shows there are likely cables feeding it so either vertical or horizontal from a device one can run cables.
However remove the device and the cables also then need removing or making dead. One can't simply connect the wires together and plaster over them.
What seems odd is normally with two way switching line would go in L1 or L2 but in your case it seems to go into Com. School boy wiring would use com
but logistics make this unusual with real wiring.
So it would seem you have some investigation to do. Glad your doing it and not me as once we enter DIY wiring there is no convention and so every wire needs ringing out and a diagram making to show what you have.