JCT DB16: If a contractor brought on to site materials due to a later potential supply issue does this come under "on-site prematurely" rule and therefore he would not get paid?

In the current Covid-19 circumstances if a contractor brought on to site materials due to a later potential supply issue does this come under “on-site prematurely” rule and therefore he would not get paid?

Under Option B the Contractor can claim the cost of Site Materials and Listed Items. See clause 4.13.1.2/3. Under Option A only Listed Items can be claimed although there is potential to claim for some elements under Option A if JCT Fluctuations Option C is applicable.