You can use the dir function to list all the txt files in the folder and its subfolders.
mytopleveldir = "C:\path\to\my\toplevel\dir";
alltxtfiles = dir(fullfile(mytopleveldir,'**','*.txt'));
pat = {'pt1' 'pt2' 'pt3'}; %etc
filter = startsWith({alltxtfiles.name},pat); %use appropriate filter to get files of interest
alltxtfiles = alltxtfiles(filter);
alldata = cell(length(alltxtfiles),1);
for i = 1:lenght(alltxtfiles)
% use your import function or readtable
alldata{i} = readtable(fullfile(alltxtfiles(i).folder,alltxtfiles(i).name));
end
% concatentate data based on your data structure
alldata = vertcat(alldata{:});
