I've come up with a 1-5 scale that can be used to "grade" character names, etc. on how well a name fits the character's generation and/or time period. Since on several name sites I've heard comments on how sometimes characters have names that are unlikely based on the chronological setting, ranging from the totally unrealistic to the plausible but less likely, I thought I'd create a scale to rate the various degrees of anachronism.
1 = The most egregious anachronisms, those with characters named something that usually wouldn't have even been in the first name lexicon of the time. Examples would be medieval females named Shannon or Taylor, or in modern times even a Gen-X or older Jayden or (female) Madison. By their nature these kinds of anachronisms usually happen in one direction only (named something ahead of the setting's time rather than behind).
2 = Characters named something that, although in the name lexicon, would be very unlikely for someone of the character's generation. Examples would be a modern girl named Agnes, or the Samantha mentioned in this post on Laura Wattenberg's blog. In general at a minimum the name would have to be out of the Top 1,000 for the character's cohort (and if the name was never very popular to begin with it would have to be even lower).
3 = Characters with a name that is unlikely but not totally out of the woods. For a name that reached the point it was/is an "everyday" name for a particular generation, this would typically represent the time it was below about the #100-200 mark but still in the Top 1,000. An example would be a Baby Boomer named Jacob, or Verizon's "Susie's Lemonade" commercials.
4 = Characters with a name that would be less likely for his/her generation (as compared to another one) but still perfectly plausible. An example is baby Amy on Up All Night (Reagan and Ava's names are borderline between a 2 and 3). Amelia on Private Practice also gets a 4 (though if the name keeps climbing the charts that might have to get downgraded to a 3 as Amelia becomes a "2010s name"; on the other hand Addison gets a 1!). For names that became very popular at a particular time, this would typically be when it is/was less popular but still in the Top 100-200 or so.
5 = Name fits the character's generation just about right. Although some name-nerdy authors might try to give all the characters "5" names, that might actually be "over-realistic" (especially if the story is intended to remain popular throughout time, rather than marketed mainly for a particular era). With stories that are destined to become classics, as well as those set in the distant future, it would be best to avoid too many names from any one era.