I have checked a number of mehudar pairs of tefillin recently where the shel yad has been written on more than one piece of klaf.
My understanding based on the Mishnas Hasofer was that this is kosher lechatchila but not mehudar.
Looking again at the Mishnas Hasofer (Siman Chof - Biur Hasofer - Vehaminhag ledovkom) he concludes - Therefore it would
appear that parshiyos that are glued are kosher lechatchila without any
doubt, however they are lacking in hidur and mitzva min hamuvchar.
Searching the forum I came across the following post from Reb Moshe Weiner a couple of years ago. (July 17 2012)
Question: Are parshiyot of yad on klaf that was glued from 2 pieces,
[the kadesh, vehaya and shma, where on the first klaf, and the last
parsha vehaya im shamoa was written on another klaf, and later glued to
the first], are they kosher lechatchila?
Answer: They are kosher lechatchila. Although it is a mitzva
lechatchila to try to write all 4 parshiyot on 1 klaf as written in SA
and poskim, this is a mitzva lechatchila for the sofer to
try to produce the best yad, but if the sofer could not write all 4 on 1
piece for any reason, then the yad is kosher lechatchila as is [after
the klafim are glued as written in Rema 32:47]. There is no pgam in the hidur because it isn't on one piece. (see Mishna Berura 32:219, Mishnat Hasofer Biur Hasofer p. 236. Indeed the terms lechatchila and bdieved must be clarified, IE the oilam
in general does not use these terms with the correct meaning. In our
case, once the issue is bdieved for the sofer, then the parshiyos are
kosher lechatchila to be used).
Therefore a client/socher may not return tefilin shel yad parshiyot if they are glued on claim they are not lechatchila (unless he specified beforehand that he will only take tefilin shel yad that are one original klaf, and not glued, as the rule "tnay sh'bmamon kayom").
My question is - if someone bought tefillin assuming that they were mehudar is he entitled to ask for a new set of parshiyos? Is Reb Moshe referring only to someone who bought a pair of lechatchila tefillin or is he also talking about a person who bought a mehudar pair?
Is there a difference if the klaf is not glued but simply slotted together as in the attached picture?
Somebody mentioned to me that they saw in a Sefer that there is actually a hiddur al pi kabollah to write the shel yad on two klafim. Has anybody since this written anywhere?