So are Ineos not pro-actively contacting customers themselves, to warn of impending deadline to make changes?
No they don't seem to be doing this, either the Agents are doing it off their own backs, or are getting a prompt from Ineos to do it.
According to the process communicated to owners directly by Ineos, the trigger should be the issuing of the contract:
From "The countdown to ordering..." email dated Friday 22nd April 2022:
"you’ll still be able to make minor changes to your specification until closer to your production date. At this point we will, of course, need you to sign a sales contract as we lock your Grenadier specification into the production schedule."
"How do I sign the vehicle contract?
We will contact you around 60 days before the start of your Grenadier’s build to request an eSignature of your vehicle contract."
"Can I change my configuration after ordering?
You can make tweaks right up until you sign your vehicle contract, but it may have an impact on your production slot. The factory don’t want us changing engines, gearboxes, interior trims but you can change your paint colour or chosen accessories, for example. Our customer service centre is on hand to help get it sorted."
So the issue seems to be that Ineos are not issuing the contracts in time but insisting that the 60 day lock remains in place.
The best advice seems to be if you want changes to your spec get them in as soon as you can, until Ineos smoothes this wrinkle out.