From the date that the offender was sentenced, last year, they are (or were) officially serving their sentence for a full 6 month period. (i.e. even when they were released from prison, they were still technically serving part of the 6 month sentence, but on licence).
If they were sentenced in, say, February last year, their licence would have expired during October, so any recent offence would not be a breach of their licence. However, if they were sentenced, say, in November, their licence would not expire until May, so any recent offence would breach that licence.
So, if the date of the most recent offence was within 6 months or the date that they were originally sentenced, they'll be recalled to prison. Otherwise, they won't. (I'm assuming that the offender was not held in custody prior to the court case, which would seem to be unlikely).
Chris