Unless you have a valid class/type rating for the aircraft, you cannot fly it.
Additionally, since EASA Part-FCL has been implemented, there is clearly visible on the licence for which aircraft you have the IR, e.g. you may have A320/IR but only SEP(LAND) or MEP(LAND), which prevents you from flying IFR in SEP or MEP aircraft.
If you want to use IFR credits from your A320 proficiency check towards SEP/IR or MEP/IR, there are some currency requirements - look it up in Part-FCL.