Tried upgrading to KSP 1.4.5 with KSPIE 1.19.4. A bunch of old craft wouldn't load up and KSP.log presented with errors similar to the following:

[LOG 20:08:04.209] PartLoader: Compiling Part 'WarpPlugin/Parts/Radiators/Microchannel/radiator-microchannel-1/KspiMicrochannelRadiator1'
[ERR 20:08:04.209] PartCompiler: Cannot clone model 'HeatControl/Parts/Radiators/radiator-microchannel/radiator-microchannel-1' as model does not exist

[ERR 20:08:04.209] PartCompiler: Model was not compiled correctly

[ERR 20:08:04.209] PartCompiler: Cannot compile model

[ERR 20:08:04.209] PartCompiler: Cannot compile part

the .mu and .dds files are indeed missing: the "HeatControl" folder does not exist. Copying the files over from my older copy of KSP 1.2 resolved the issue.

Due to license constraints, you need to download the mod HeatControl seperately to make use of KSPIE revisioned microchannel radiator

Alright, thanks. If this is well documented then let's call me dumb and close this issue.