Canon 69 addresses only the Reader. Why only him? Because it is assumed that a deacon or priest will have been married before they are ordained. This canon made me grin, although fornication is a serious subject. You see, the canon differentiates between fornication after betrothal, and simple fornication with a woman with which the Reader has no other relationship. The treatment of the Reader who is betrothed is breathtakingly light. Let him be apart from the ministry for a year is giving him just enough time to finish the betrothal period, be married, and to have a couple of months of marriage under his belt. You can almost hear Saint Basil sigh about betrothed couples who could not wait. There is an almost charming pastoral approach to this.
However, notice in that canon and the other canons, that should a Reader, a Deacon, or a “minister” be involved in fornication outside a betrothal, they are deposed and removed for life. They are still allowed to receive communion, as their deposition is already such a severe punishment that to also remove them from communion would be too harsh. Nevertheless, there is no give in Saint Basil when he writes about fornication outside of either cohabitation or betrothal. Note that the person cohabitating may still serve a multi-year penalty, but it is not a lifetime or prohibitive penalty. I say "may still serve” a penalty because it is not fully clear (without more study on my part) as to whether Saint Basil would have treated the cohabiting couple more like the Reader and his betrothed or more like a simple fornicator.
The person who serves the least penalty is he who commits fornication with his betrothed. And his only penalty is to not be allowed to serve “up front” until after his marriage. Most of us today would agree with that very light approach toward engaged couples who fall into that particular type of sexual sin. It is not that we approve of fornication in any way. Rather, it is with a sigh and a recognition of how often (even back when) an engaged couple gave in to temptation. It obviously happened often enough, even among those ordained to minor orders, to need a canon written about it.
It's not surprising that Basil observed that once betrothed a lot of people just didn't wait. That doesn't mean they shouldn't have waited, but it could mean, as Steve Hays over at Triablogue mentioned about OT case law, that case law deals with situations common enough to develop a law for. The potential application to canon law may be similar, though of course I'd defer to my Orthodox friends and associates as to whether or not I've accurately inferred this.