The TDA7000 chip only has a FLL inside of it. The demodulator circuit sends out an error voltage if the manual band tuning capacitor does not center the LO oscillator at the FM station's center frequency. That error voltage then slightly retunes the LO oscillator's center frequency up or down 300KHz to get the best FM station reception. As you then tune the manual band tuning capacitor (or it drifts with time or temperature), the FLL error voltage will keep the FM station tuned to its center UNTIL the FLL runs out of voltage range. At that point the FM station suddenly "breaks lock" and gets a lot of static. If you manually retune the band tuning capacitor, up or down, then at some point the FLL can reaquire the FM station and it all starts to work again.
A different type of chip could use a PLL to lock the LO oscillator irregardless of if the FM station is properly centered or not. For this to work, you are couting on the FM station to be precise in frequency, and the crystal oscillator in the PLL lock to be precise in frequency.
IF you wanted to use both a PLL and a FLL, you would need TWO independent circuits. You would use the PLL to downconvert the FM signal to a lower IF frequency--say 10.7 MHz (where there could be a +/- frequency error present). Then you would use a second circuit containing a FLL to further downconvert the IF frequency to the demodulator. In this way the two circuits, PLL and FLL, do not fight each other.