On Stephenson-Siemens on-line game - there is a builders yard, currently having contracts with 2 quarries and 3 forests. But it does not accept stone... If I recall correctly the game started in early 1800's and the builders yard was built quite soon in the game. So it may have been accepting stone at that time (BuildersYard1800), but was most probably upgraded to BuildersYard1850 since then. Now it does not accept stone any more, but the quarries are still listed as contracts. Fortunately I tried delivering stone on an offline copy, and was wondering why none is sent...
Imho such contract should be dropped if the list of input goods changes due to upgrade.
Also happens with breweries, upgrading from wood to steel, and with many other industries when wrought iron gets replaced by steel. In these cases, when one upgrades, this usually results in nonfunctional chains. In these cases, either the whole chain should upgrade, or the whole chain should be deleted doe to not being compatible anymore (this would make upgrades of these industries meaningless though).