"This Would not work if any of the cases under the IF & elseif aren't satisfied then this table will not be Concatinated. "
That's true, and in fact at most one if or elseif condition will be satisfied in each iteration of the inner (J) for loop, which means that at most one of Eco_Table, Per_Table, Standard_Table, Tanker_Table, Off_Table, Down_Table, Heavy_Table will be defined on the first loop iteration, so that loop will always fail with an error on the Sumary_Table line on its first iteration because most if not all of the variables it uses are undefined. Also, you're attempting horizontal concatenation, which won't work due to the same table variable names existing in each table. (And even if that concatenation worked, Sumary_Table is overwritten on each iteration.)
Now, what to do instead? Well, it's really not clear exactly what you want Sumary_Table to contain. Maybe something like what follows. Note that the if/elseif blocks are all doing basically the same thing, so it's easy to generalize them using Pattern_For_List{J} rather than the hard-coded values "_02", "_03", etc. (and no need to tranpose Pattern_For_List either, not for this anyway).
pathn = '.';
F = dir(fullfile(pathn,'*.txt'));
filelist = fullfile({F.folder},{F.name});
N = numel(filelist);
Summary_Table = cell(N,1); % cell array of tables, one per file
for K = 1:N
filename = filelist{K};
file_Details = importdata(filename);
Data_in = readtable(filename, 'Delimiter',{',',';',' '});
is_empty = strcmp(Data_in.Var1,':').';
s_idx = strfind([false is_empty],[false true]);
e_idx = strfind([is_empty false],[true false]);
for ii = 1:numel(s_idx)
Data_in{s_idx(ii):e_idx(ii),1} = Data_in{s_idx(ii)-1,1};
end
All_Para = Data_in.Var1;
Slot_PG_List = {'C_PG_SlotPGID_00';'C_PG_SlotPGID_01';'C_PG_SlotPGID_02';'C_PG_SlotPGID_03';'C_PG_SlotPGID_04';'C_PG_SlotPGID_05';'C_PG_SlotPGID_06'};
Compare_PG_List = extractAfter(Slot_PG_List,"SlotPGID_");
Compare_Slots = contains(All_Para,Slot_PG_List);
Slot_Data = Data_in(Compare_Slots,:);
Slot_Data_Values = lt(Slot_Data.Var4,255);
Slots_Active = Slot_Data.Var1(Slot_Data_Values);
Pattern_For_List = extractAfter(Slots_Active,"SlotPGID");
Extracting_List = find(endsWith(Data_in.Var1,Pattern_For_List));
Extracting_List_Data = Data_in(Extracting_List,["Var1","Var3","Var4","Var7","Var8"]);
NP = numel(Pattern_For_List); % cell array of tables, one per suffix
T = cell(NP,1);
for J = 1:NP
idx = find(endsWith(Extracting_List_Data.Var1,Pattern_For_List{J}));
T{J} = Extracting_List_Data(idx,:);
end
Summary_Table{K} = vertcat(T{:}); % vertically concatenate to make a summary table for file K
end
disp(Summary_Table)
% optionally vertically concatenate to make a summary table for all files
Summary_Table = vertcat(Summary_Table{:});
