Erie had covered hoppers that were PS-2 knock off's built by Greenville.
Erie had covered hoppers that were built by ACF, but based on a General American design.
Erie had covered hoppers that were ACF clones, but were built at Greenville.
Erie also had covered hoppers that were built at their Dunmore shops from kits.
Looks like they just used the plans, but had someone else build them.
Err, not that I want to defend MT in any way...