"Codes" is correct when the intended meaning is access codes and the like, but not for source code, which is a non-countable noun.
I think the uptick is due to the increased number of participants who are not native speakers, mainly from Asia and eastern Europe I would presume--I'm not a native speaker either but the distinction between countables and non-countables is natural to me, coming from another Germanic language.
I think the uptick is due to the increased number of participants who are not native speakers, mainly from Asia and eastern Europe I would presume--I'm not a native speaker either but the distinction between countables and non-countables is natural to me, coming from another Germanic language.