Select Bits in 4-to -1 MUX
Yes, you can have that. You'll just have some selection combinations that make the same selection. For instance:

module mux_4to1(Y, A, B, C, D, sel);

output [15:0] Y;
input [15:0] A, B, C, D;
input [2:0] sel;
reg [15:0] Y;
always @(A or B or C or D or sel)
  case ( sel )
    3'b000: Y = A;
    3'b001: Y = A;
    3'b010: Y = B;
    3'b011: Y = B;
    3'b100: Y = C;
    3'b101: Y = C;
    3'b110: Y = D;
    3'b111: Y = D;
    default: Y = 16'hxxxx;
  endcase
endmodule