IIRC, One of the Devs mentioned that a production line which lacks any of the required resources will not see improvements in its gearing efficiency bonus/malus..
That is part of the reason I referenced flip flopping.
1. There was indication by devs pre WWW that you needed resources to gear up.
2. In WWW1, there was a tool tip that reported no gearing increase without resources.
3. By WWW4, the tool tip disappeared.
4. By WWW4, it was obvious the rule was not in effect. Germany has made no effort to get rubber during the entire game (all 7 videos). But even without rubber, Germany achieved good gearing rates for his airplanes and motorized units.
5. In WWW7, there was a gearing reset which allowed a glimpse into the increase rate by comparing different units started at the same time, and UK/Germany resets. Late in the video, Germany clearly shows its tactical bombers without rubber are lagging behind the anti-tank weapons which have all the resources. Some quick number crunching with estimates indicated that a 1/3 rate loss make sense.