Vlachs today no longer exist in Slovenia, Croatia, Bosnia and Herzegovina, Montenegro while in Serbia exist smaller Vlach population. Primary historical sources mentione Vlachs in Croatia and Bosnia and Herzegovina and this was period shortly before the Ottoman occupation and mostly during the Ottoman occupation.

The historiographic framework on this matter says the following:

Ivo Banac, Croatian-American historian in book "The National Question in Yugoslavia: Origins, History, Politics" says the following(page 43): "Orthodox Slavicized Vlachs gained Serbian national consciousness due to their affiliation with the Serbian Orthodox Church. As a result of Vlach assimilation, Serbian pockets were created among Croats."

Noel Malcolm, English academic in book "Bosna kratka povijest" says the following(page 108): "Calling someone a Serb today means using a term created in the 19th and 20th centuries based on a shared religion, language, history and personal sense of national belonging. Today's Bosnian Serbs can freely present themselves as Serbs, regardless of their Vlach origin."

Ilona Czamańska, Polish historian in scientific paper "Vlachs and Slavs in the Middle Ages and Modern Era" (page 19) : "Majority of Serbs from the Republika Srpska of modern Bosnia is of Vlach origin, as well as the majority of the population from Bosnia and Herzegovina in general"(This also applies to the entire Western Balkans as a mixture of Slavic and indigenous population), but also states that "there are no direct sources to support Vlach colonization of these lands."

Karl Kaser, Austrian historian and expert on the Military Frontier, in book "Household and Family in the Balkans: Two Decades of Historical Family Research at University of Graz" (page 114): "it is possible to show that Serbs and Vlachs were different in the 13th century, while a little later the Vlachs were Serbinized... in that assimilation process, many Vlach terms related to animal husbandry were adopted into Serbian,Albanian and Greek languages"

Vjeran Kursar, Croatian historian in scientific paper "Being an Ottoman Vlach: On Vlach Identity (Ies), Role and Status in Western Parts of the Ottoman Balkans (15th-18th Centuries)" (page 124) "While the importance of Catholic or Muslim Vlachs, or other, non-Serbian elements should not be underestimated, it seems that the greatest part of the Vlachs in the western Balkans was Orthodox Christian and Serbian(ised), often still bilingual"

Sima Ćirković, Serbian academic in book "The Serbs" (page 5): "The fact that in the state of Serbian rulers there is, and massively, another ethnic element, it was difficult to reconcile with the "genealogical" hypothesis,according to which the inhabitants of the Serbian state were descendants of Serbs who had settled on the Balkan Peninsula.
In advance, it was concluded(part of Serbian historians) that the name Vlachs did not describe ethnicity but status; it was correctly noted that the Vlachs were herders and the Serbs were farmers, but it did not follow that the Vlachs were Serbs who are herders.

As far as we can see, the historiographic framework is mostly oriented towards the Orthodox Vlach population, which becomes Serbs although part of the Vlachs were Muslimized and Catholicized who later became Bosniaks or Croats etc.

This topic should be open in the context of what the new genetics can say about Vlachs, from where they come to Croatia and Bosnia and Herzegovina or Slovenia, Montenegro, etc. Do they come at all, given that the Vlach name could have spread to the autochthonous population as well. We know about the example of the Republic of Venice for whom all the inhabitants of the Adriatic coast are Morlacs, i.e. Vlachs regardless of religion. There were also examples from the Hungarian side in this context.

What we have for now although a bit outdated is paper: Marjanović et al. (2005) "The Peopling of Modern Bosnia-Herzegovina: Y-chromosome Haplogroups in the Three Main Ethnic Groups" where Bosnian Serbs have E1b haplotype as the second in the population which could indicate Vlach origin ie direction of movement from the Albanian-Montenegrin mountains, possibly also the Bulgarian direction of certain branches.

Also some I2a branches may indicate some Vlach migration from direction of Greece or Bulgaria. I-Z17855 https://www.yfull.com/tree/I-Z17855/ https://www.yfull.com/tree/I-FT109387/