NPR discusses the issue
@JimFord99 was talking about,[1] though not specifically with metoclopramide. In the US, drug companies have little incentive to investigate increasing shelf life numbers after their first numbers are approved. As a result, some drugs have shorter official expiration dates than necessary.
ToxNET, a government-funded website, gives a 3 year shelf life for metoclopramide hydrochloride tablets.[2] I haven't had any luck finding longer numbers in reliable sources.
I guess it's safest to go with the expiration date unless you can find more compelling evidence otherwise.
References
[1] Allen, Marshall, "That Drug Expiration Date May Be More Myth Than Fact," NPR.org. [Online]. Available:
https://www.npr.org/sections/health...ug-expiration-date-may-be-more-myth-than-fact. [Accessed: 26-Oct-2019].
[2] "TOXNET." [Online]. Available:
https://toxnet.nlm.nih.gov/cgi-bin/sis/search2/r?dbs+hsdb:@term+@rn+@rel+364-62-5. [Accessed: 26-Oct-2019].