Today is the 98th anniversary of Tokugawa Yoshinobu 徳川慶喜's death. Yoshinobu was the last ruler of the Edo shogunate, but managed to avoid being assassinated or executed, moved to Shizuoka, and enjoyed a long and uneventful retirement.

Well, I say "Yoshinobu"... actually, the issue of his name is not so clear. Japanese Wikipedia sez:

「慶喜」は、「よしのぶ 」あるいは通称として「けいき 」（有職読み）とも読む。将軍在職中、江戸幕府の公式な文書等には「よしひさ 」と読んだとの記録が残っている。本人によるアルファベット署名や英字新聞に「Yoshihisa 」の表記も残る。 ... 出身地である水戸では「よしのぶ」と呼ばれる事が多いが、余生を送った静岡では「けいき」と呼ばれる事が多い。

生前の慶喜を知る人によると、慶喜本人は「けいき様」と呼ばれるのを好んだらしく、弟・徳川昭武に当てた電報にも自分のことを「けいき」と名乗っている。慶喜の後を継いだ七男・慶久も慶喜と同様に周囲の人々から「けいきゅう様」と呼ばれていたといわれる。「けいき様」と「けいきさん」の2つの呼び方が確認でき、現代においても少なくなりつつあると思われるが「けいきさん」の呼び方が静岡に限らず各地で確認できる。司馬遼太郎は「『けいき』と呼ぶ人は旧幕臣関係者の家系に多い」とするが、倒幕に動いた肥後藩関係者でも使用が確認できる。

"慶喜" was read both "Yoshinobu" and, alternatively [as a tsūshō 通称] "Keiki" (this being the yūsoku yomi 有職読み). Some records indicate that while 慶喜 was shōgun, his name was read "Yoshihisa" in shogunate documents. The romanization "Yoshihisa" also appears in English newspapers and in 慶喜's own signature. ... in Mito, where he was born, he is usually referred to as "Yoshinobu," but in Shizuoka where he spent his retirement, "Keiki" is more frequently used.

According to those who knew 慶喜 while he was alive, he himself preferred to be called "Keiki-sama," and in telegrams to his younger brother Tokugawa Akitake identified himself as "Keiki." Similarly, 慶喜's heir and seventh son, Yoshihisa [慶久 — different second character], is said to have been called "Keikyū-sama" by those around him. "Keiki-san" and "Keiki-sama" are both attested, and although contemporary usage is waning, "Keiki-san" is attested not only in Shizuoka but in a range of locations. [Author of carefully-researched historical fiction] Shiba Ryōtarō 司馬遼太郎 says that "Most of those who call him 'Keiki' are from families connected with the former shogunate," but the usage is also attested among those connected with the Higo Domain, who worked to topple the shogunate.

Like I said: legalistic system. You can't argue from first principles. All you can do is cite precedent and hope for the best.