The various discussions show that farther in the past, there were a number of different minhagim. It was not always the case that weddings were not held for the entire period (though that is one minhag as shown by Rabbi Kaganoff).
Rabbi Kaganoff points out that no matter what minhag is being observed, it is still basically a method of counting 33 days.
Rav Moshe Feinstein points out that although these customs differ which days are considered days of mourning, the premise of most of the customs is the same: Thirty-three days of sefirah should be observed as days of mourning in memory of the disciples of Rabbi Akiva. In Rav Moshe’s opinion, these different customs should be considered as one minhag, and the differences between them are variations in observing the same minhag (Igros Moshe 1:159). This has major halachic ramifications, as we shall see.
The minhag of the "entire" period was actually the 33 days excluding Shabbos, Chol Hamoed, and Rosh Chodesh.
This approach is based on an early source that states that Rabbi Akiva’s disciples died only on the thirty-three days of sefirah when tachanun is recited, thus excluding the days of Shabbos, Yom Tov, Chol HaMoed, and Rosh Chodesh (Bach, quoting Tosafos). If one subtracts from the forty-nine days of sefirah for the days of Pesach, Chol HaMoed, Rosh Chodesh, and the Shabbosos, one is left with thirty-three days. It is on these days that the mourning is observed. (This approach assumes that in earlier days they recited tachanun during the month of Nisan and during the several days before Shavuos.)
Attending a Wedding during one’s Sefira
One who is during his sefira may still attend a wedding of someone who is making a wedding when the bal simcha is not holding sefira. This is even if he wants to dance and listen to music there.[Divrei Yoel 1:26:1, Natei Gavriel Pesach 3:page 214:footnote 17 (minhag in Skver), see Lag B’omer page 178:footnote 31.]
Marriage During the Omer Counting Period
It is the opinion of some authorities that only "optional" marriages
are to be avoided - i.e., marriages wherein the groom was previously
married and has fulfilled the Torah obligation to have children. One,
though, who has not yet fulfilled this commandment, say these
authorities, can marry during the Omer counting period. This is
because the commandment to marry outweighs the custom to mourn (Pri
Chadash). In practice, however, later authorities agree that the
custom calls upon even those who have not yet fulfilled the
commandment to reproduce to refrain from marrying during this period
(Mishnah Berurah 493:1).
If an individual is invited to a wedding on one of the days which,
according to his own custom, it is forbidden to marry, he is permitted
to attend the wedding, to partake in the meal, and to make the bride
and the groom happy by dancing in their honor (Iggrot Moshe, Orach
Chaim 1:159; see also Piskei Teshuvot 493:13).
Rabbi Kaganoff says
Can One Change From One Custom to Another?
We would usually assume that someone must follow the same practice as
his parents – or the practice of his community – because of the
principle of al titosh toras imecha, “do not forsake the Torah of your
mother (Mishlei 1:8)”. This posuk is understood by chazal to mean that
we are obligated to observe a practice that our parents observed.
However, Rav Moshe Feinstein contends that since the different customs
that are currently observed are all considered to be one minhag,
changing from one custom to another is not considered changing one’s
minhag, and it is therefore permitted. There is ample evidence that
other, earlier poskim also agreed that a community may change its
custom how it observes the mourning days of sefirah (see Shut Chasam
Sofer, Orach Chayim #142). According to this opinion, the specific
dates that one observes are not considered part of the minhag and are
not necessarily binding on each individual, as long as he observes
thirty-three days of sefirah mourning.
Attending a Wedding During One’s Sefirah Mourning
If a friend schedules a wedding for a time that one is keeping
sefirah, is it permitted to attend? One is permitted to attend and
celebrate a wedding during his sefirah mourning period, even listening
to music and dancing there (Igros Moshe 1:159).
Thus, although I am required to have a mourning period during sefirah
of at least thirty-three days, I may attend the wedding of a friend or
acquaintance that is scheduled at a time that I keep the mourning
period of sefirah. However, Rav Moshe rules that if one is going to a
wedding on a day that he is keeping sefirah, he should not shave,
unless his unshaved appearance will disturb the simcha (Igros Moshe