The '30' suffix that you have identified is the Boeing customer designator assigned to Lufthansa, for example the 737-530, all the Boeing aircraft in the Lufthansa fleet have a '30' suffix, 747-430, 747-230B, etc..
All Boeing customers have their own designator code, for example:
Northwest Airlines is '51'
British Airways is '36'
Iberia is '56'
United Airlines is '22', and so on....
An aircraft designated as a 747-287B, but in say Virgin Atlantic Colours may have been originally delivered to Aerolineas Argentinas (the airlines code is '87') and then acquired by Virgin at a later date. The designator code never changes, even if an aircraft does change owners/operators.
It is interesting to note that Airbus Industrie do not assign customer codes to their aircraft, they instead have a number relating to the customisation of the aircraft (its fittings, etc) so in this case a number of different airlines can operate the same type of aircraft with the same customisation code.
I love it when a plan comes together