What’s the din if b’dieved a tzibur was not able to read parshas shekalim on the appropriate Shabbos – can they do a makeup next Shabbos or some other time?
At first glance one would think that the 4 parshiyos are just like the special readings done on any Yom Tov. If, for example, you don’t do the correct Torah reading on the first day of Pesach, you can’t make it up the week after Pesach. So too, if you miss reading shekalim on the appropriate week, there is no makeup.
R’ Akiva Eiger paskens this way, but the Eishel Avraham and Maharam Shi”k disagree. The gemara (Meg 29b) compares the takanah to read shekalim to the din of learning hilchos yom tov 30 days before a chag. Since the new shekalim had to be brought by Rosh Chodesh Nisan, the reading was done 30 days earlier to give people advance notice to prepare. Obviously if you don’t start learning hilchos Yom Tov exactly 30 days before a chag, that doesn’t mean you should give up – aderaba, start the next day or as soon as possible (Shu”T Maharam Shi”K 365).
It sounds like the machlokes revolves around the classic issue of whether the reason behind a takanah impacts the din’s parameters. According to R’ Akiva Eiger, there was a takanah to read shekalim on a specific shabbos – the reason behind the takanah does not change anything. According to the Maharam Shi”k, we take the reason into account.
If you want to go a step further, perhaps the Maharam Shi”k would say that if indeed the reading of shekalim belonged on the list of takanos of special Torah readings for special days, then R’ Akiva Eiger would be right. But it doesn’t belong on that list. The takanah is not a din in kri’as haTorah – it’s simply a reminder. It’s the equivalent of the gabai giving a klap on the bimah and yelling out “Don’t forget whatever.” There is no halachic structure called “give a klap on the bimah,” so Chazal used the structure of kri’as haTorah instead to accomplish the same goal. The gemara’s comparison to the din of learning hilchos hachag before Yom Tov is not just a superficial analogy to make the point of when shekalim should be read -- it's telling us that the two halachos are fundametally similar. Just like learning hilchos ha'chag is just a means of getting us in the mindset for Yom Tov, so too, reading shekalim is just a means to an end, a utilitarian reminder. Not so the kri'ah on Yom Tov, which is an expression of and helps establish the underlying kedushas hayom (for more on that, see this post).