vanredni
extraordinary would be the word, but it acquired a meaning in english which is far from its latin origin; 'vanredni' is anything that occurs outside the regular order, including 'ambassador extraordinaire', and 'vanredni student' (part-time student), 'vanredni voz' (special one-time train), 'vanredno stanje' (extraordinary powers enabled because of a disaster or coup), 'vanredni izbori' (snap elections)
disorderly - almost there, 'vanredni' is opposite to regularly scheduled, except 'disorderly' describes conduct, not an occurrence outside of scheduled. Ditto for 'unorderly'.
out-of-order would be a good literal translation (out-of-row also), if it didn't mean 'malfunctioning'.
spot - as in 'spot check', when there's a regular one and then one can be made on the spot, beyond and above the regular one. Too bad that spot, even as an adjective, means dozen other things.