One of the arguments that is made on behalf of a woman who received permission from the beit din to remarry, only to discover that her husband was still alive, is presented by Rav Sheshet. The argument is a simple one – mai havei lah le-me’evad? – what could she possibly have done to protect herself?
In an attempt to show that mai havei lah le-me’evad is not a sufficient argument to free the wife from her responsibility, Ulla brings another case where the woman finds herself in a similar predicament, through no fault of her own. If a woman receives a get – a divorce document – which had the date written incorrectly, i.e. it was dated based on a malkhut she-eina hogenet – according to the Median era, or according to the Greek era, according to the era of the building of the Temple, or the destruction of the Temple – the divorce is invalid; if the woman remarried based on that get, she will need to get divorced from both her original husband and her second husband.
The Gemara responds to Ulla’s argument by saying that in this case there was something she could have done – she should have arranged for the get to be examined by a competent person.
The concept of a malkhut she-eina hogenet – an “unsuitable kingdom” – is explained by Rashi as referring specifically to Rome, which was seen by the Sages as being an uncultured society, its strength and stature notwithstanding. The basic rule is that the date must match the requirements of the local government; thus, writing the date based on a different country – and certainly if it was based on an historical event or a government that no longer existed – would invalidate the document.
With regard to the rule that the date in a divorce document needs to be precise and recognized by the government, Tosafot explain that, given the importance of such a document, the civil authorities were exacting in the way it was written, which made the Sages insist on a valid date.