Solar panel rating is confusing at best.
The standard insolation is 1000Wper sq Metre, something that many of don't see often if ever.
The other catch is that they measure the output at a specific panel temperature which is low ( 25 deg C ?)
In most places a panel seeing the standard insolation will be much hotter than the test temperature.
It is not likely that many will ever see the rating of a panel that meets its spec.
This is at the maximum power point and power into a battery will be a fair bit less.
Decent manufacturers get close to their rated figures but I have seen claims that not all samples of panels meet the rated output.
Cheap, mostly amorphus silicon panels, fall way below claimed spec, and they get away with it because the user has no means of proving them wrong. Small low power panels are less likely to be checked than large and expensive ones.
I think you are unlucky and have some that are way worse than you would reasonably expect. To prove it you will need to send them to someone certified to test them and it will cost you money and hassle, the makers are relying on this.
I think these are so obviously below spec that you would have been justified in taking them back but you should have done it immediately.
The world is full of scams, wind power is worse than solar.
Flux