"What if" contractor 6 months behind, then essential procurement item becomes 9 months behind? Is it unfair construction acceleration if the contractor is still pushed for overtime and accelleration even though there is a worse delay than the original - & that being a essential procurement item (like elec switch gear) that cannot be accellerated? They are late, but they are also then hurring just to wait...? Is that unfair constructive accelleration - I am guess not but I do not know. I assume the Owner goes after the GC for LD's and the GC goes after the supplier.
The answer to this question depends on who's responsible for the risk of each delay. If the client has some responsibility for one of the delays your are looking at a concurrent delay situation, if the contractor is responsible for both, the contractor has a problem.
Concurrent delays are a complex issue affected by the contract and by diffeent interpretations of law in various jurisdictions see: https://mosaicprojects.com.au/PMKI-ITC-020.php#Concurrent