I'm torn because the other suppliers that are still on track with the original timeline might run in to issues of their own so perhaps working to the original timeline is a good way to reduce risk. However, pressuring the suppliers that are still on track with the original timeline to stay on track to the original timeline feels somehow wrong. Perhaps if they were aware of our new timeline they could change priorities and run their business more efficiently
I can think of only one reason why you would inform and alter the schedule of one supplier when another is late: dependency, in which case you would have integrated the schedules and everyone involved will see the variances and impacts accordingly.
All projects produce variances. A variance free schedule is a fake one. I cannot imagine trying to recalibrate other schedules when one schedule produces a variance, especially since that variance may disappear and another appears. Ever day, you would be rebaselining schedules and chasing what is mostly random.
"The many are smarter than the few" is a mantra I've taught to my agile teams for years. There is even a book, The Wisdom of the Crowd, founded on this very concept.
I would promote full transparency for the very reason that by doing so you tap into the greater whole. One person can't see all the moving pieces and all the relationships. By sharing with all your suppliers you may find someone has a solution to help that other supplier.
This is completely counter to how I used to work, as a traditional project manager, where I had an almost institutional distrust of everyone on the team and thought things like "If I tell them they have more time, they will just use it."
Instead, set regular (weekly or every two weeks) goals and checkpoints, be fully transparent and trust your team (and suppliers) to be professional. I've been amazed at the results as I shifted from my old command and control project management to facilitating goal focused teams.
Primarily it depends upon how mature your suppliers are. If your suppliers are mature, then can trust them to see the whole picture and deal with the delays in a way that is best for them and all concerned. If they are not mature, then they may be tempted to simply use up any new time, or use it to mask their own issues that they have not yet informed you about.
However, regardless of how mature your suppliers are, if there are dependencies between your suppliers then you must inform the impacted suppliers as a minimum.
Ultimately, you need to do what is going to give your project the best chance of success. While notifying other suppliers that the baseline has moved may help them run their business more smoothly, consider:
- It increases risk by complicating the situation. Your other suppliers now have a change to their deadline, that can lead to new risks that wouldn't have occurred had you left it as it was
- Leaving the current timeline in place gives other suppliers a bit of bonus wiggle room if something unexpected should occur. If you give someone extra time to deliver, they'll use it
- As @DavidEspina has said, there's additional overhead in constantly changing timelines for changes such as this
Simply put, don't make a change unless there's a definitive reason and benefit for that change; I can't see any particular benefits to your project by alerting your suppliers to this info.