Two approaches proposed: the literal one and the circumlocution (and there's nothing to stop you using both).

1) Captive lot: the main contractor no choice. "Captive" is a perfectly good word to use -- see the phrase "captive consumer".

See this H&M example:
https://www.arteliagroup.com/fr/offre/nos-domaines-d-activit...

Right at the bottom of the main text: "Pilotage des lots captifs H&M."

Presumably the H&M Group people at national or regional come in and say, uniformise the overall look of the shop, provide standard clothes hangers, shelves, point-of-sale material, etc., like all multinationals do.

"captive lots" is used at the bottom of the main text on this page, which is a reasonably good translation, done for a multinational company.


2) Circumlocution -- describe the above arrangement as concisely as possible.


In a manufacturing context, perhaps captive lots would refer to services provided under service provider agreements, maybe plant & machinery matters that can only be dealt with by given companies, government agencies, gas and electricty (ENEDIS and GRDF).


The key points from the FR>SP question posted by Phil below automatically translate as

"except exclusive lots from specific suppliers"

and

"except lots reserved to a supplier"

Not much useful in the FR-GER question, something about trades.


Conclusion: I think in English we would just say "oversight of all suppliers" instead of using the narrowing term "lots captifs". (You have to oversee them whether they're captive or not, would be a practical approach.)

The term "captive lot" is not used very much in English, so you need an explainer with it.

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Note added at 3 hrs (2021-05-05 12:49:50 GMT)
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FORGOT THE LINK:

"captive lots" is used at the bottom of the main text on this page, which is a reasonably good translation, done for a multinational company.

https://www.atixis.com/en/epc/

"[...]...coordination of the various stakeholders on the site (BC, CSPS, subcontracting companies, ***captive lots***, third parties, etc.)"

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Note added at 28 days (2021-06-02 23:24:46 GMT) Post-grading
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To Jane: you're welcome. I worked hard on that question, it was interesting!