Seems the FIA have confirmed a loophole in the Engine homologation regulations that points out the letter of the rules only states the date of the submission of the design is only stipulated in the first year, the spirit of the rules was intended the date be applicable for all years, but the letter states only the first. As a result Ferrari, Renault and Mercedes can introduce their u[grades through the year, taking more time over them, however the "tokens" for each part of the engine still apply so they are still limited in the scope of what they can change (and by the number of engines they can use per season), they can just take more time in evaluating which of the changes offers the best bang for the buck.
Ironically, as this is Honda's first year they still have to submit their design in Feb, with no further upgrades in the season.