I can't speak for other parts of Europe, but in Ireland it's not rare at all. It's quite common for any given church or parish to have its own petty saint, usually the founder of that church, often known only through local tradition or brief mentions in hagiographical literature. Many of these are placed in the proto-historical 5th-7th centuries and are of fairly dubious historicity, not so much in the sense that they didn't exist, but that the later traditions surrounding their lives and genealogies were often shaped by church politics more than reality. Early Irish churches from the 7th century on tended to band together under different confederations or 'familia' ('paruchia' is another common term) headed by one mother church, with local churches and their parishes under the authority and protection of major foundations like Armagh, Kildare, Iona and the like, who of course recieved tribute from their dependencies. These relationships, which were often closely related to the relationships between secular dynasties, were justified by traditions, for the most part invented, which imagined local patron saints as junior partners or disciples of the more important saints.

You can see this clearly with Gobnait;

Móin Mór (Bairnech, Baile Mhuirne, Ballyvourney), the church and nunnery of Gobnait [Mo Gobnat] (fl. 6th cent.?) lay west of the monastery of Cork on the borders of Múscraige Mittine and Eóganacht Locha Léin. Its patron, Gobnait, is commemorated on 11 February in Félire Óengusso and was affiliated to the Múscraige. Her church never had more than local importance and Gobnait is not the subject of a life. She does appear in the life of Abbán, where she is very much the junior partner of the male saint. Furthermore, Findbarr's life lays claim to the church by asserting that it was founded not by Gobnait, but by a disciple of Findbarr. Her cult flourished there, however, and the remains of the medieval church can still be seen. Locally, the saint's day is still celebrated. Johnston, Elva. "Munster, saints of (act. c.450–c.700)." Oxford Dictionary of National Biography

So what we seem to be seeing here is two church 'familia', those of Mag Arnaide (in Wexford, founded by Abbán) and Cork (founded by Finbarr), asserting seperate traditions in order to lay claim to Gobnait's see of Móin Mór, and perhaps to episcopal authority over the Múscraige or some subset of them (this was ultimately about authority over territories and peoples, not just churches). Monasteries could go to war over this sort of stuff, as at the battle of Argaman in 764 AD. Saint's vitae were to a large extent political documents, asserting the rights of one parish over another. You wouldn't expect to see many of them written for minor saints, since they didn't have any such claims.

Just go through this list, and you'll find that most of these are just known through local traditions or brief textual mentions; https://en.wikipedia.org/wiki/Category:Medieval_Irish_saints

Also for more on ecclesiastical confederations see; Colmán Etchingham, The Implications of Paruchia, Ériu, Vol. 44 (1993), pp. 139-162