1: I concur with gringeltaube .. You could get creases / overlaps when you assemble it, which will create friction "sores" and could eventually fail.. It does depends on how far "off" the tube is, the type of use or speed it will see, and the thickness of the tube.. This is true with any size or style of tire .. Over the decades I have come across a few old 20" heavy truck tires with "folded" tubes, such as a 1100x22 tube stuffed into a 900x20 tire, and they had survived many years that way.. But those tubes were 1/4" thick heavy rubber with flaps (liners).. They don't make anything close to being that good anymore.
2: The opposite is also true in certain situations, an undersized tube can be forced to stretch to fill the space, leading to immediate failure , or a very short life...
3: We can't trust today's tubes as to their stated or stamped size, name brand, nor alleged "quality".. Mister Chicom is very happy to take our money and leave with no responsibility for our time, aggravation, tire failure, vehicle damage, or more.. We have certain politicians to thank going back many years now, but I am biting my tongue really really REALLY hard..
4: Case in point, a highly-reputable tire dealer/ commercial truck shop I know had issues with Chicom tubes labeled to be a certain size, however, were too small in girth and circumference leading to immediate failure during initial inflation... They also had issues with quality, of course... Ever since, they go to great lengths to NOT purchase chicom items, unless a customer insists on them using "economy" products.. A customer has to sign a waiver if that is the case, and the work / product is not guaranteed
5: I too had been an early victim of such thievery, having purchased online some new 9.00x16.5 tubes having the BF Goodrich name and advertised "made in usa"... The sealed bags they came in as well as the rubber was stamped 900x16.5 , but in reality were only suitable for perhaps a 5.50x16 tire.. The tubes were BF Goodrich, but on them stamped "china." Return shipping and restocking fees for a refund was almost as much as the purchase.
6: Advice for all of us, buyer be aware ... If you can, put your hands on any rubber tire-related product before purchasing
7: This advice is also for automotive electrical and plumbing items, as well as consumer goods.. Over the last 2 decades, counterfeit certifications have been discovered on many imported products, mostly coming from one country.. I have been reading about this in trade magazines since the early-2000's.. Fake UL, CSA, ASSE, IAPMO, ASME, and ASTM labeling... When caught, the manufacturers and shippers of these items continue to find creative ways to circumvent our laws while our, ahem,, public servants,, do nothing more than an occasional hand slap .. Sorry, that's my rant for the day.