Well since the "Dibble book of really important things" (Janes-Traffic Officers Companion) says
"Must bear a mark indication compliance with the British Standard OR be of a type which by virtue of its shape, material & construction could be reasonably be expected to afford protection similar to or greater than, a helmet which conforms to the British Standard, an accepted EEA Standard or of ECE regulations."
You could reasonably argue that as the DOT allowance for transfered energy to the head "measured in Gs" is less than that by 22-05, then actually your helmet offers greater
From a police perspective the legislation (as quoted) is so "fluffy" it has commonly been interpreted as "if it looks like it will do the job then....it's legal" you try prosecuting someone with a DOT helmet in the UK. The DOT specification is good enough to protect 316,218,000 residents of the USA...!