设数列\(\left\{{a}_{n}\right\} \)是首项为\(1\),公差为\(\dfrac{1}{2} \)的等差数列,\({S}_{n} \)是数列\(\left\{{a}_{n}\right\} \)的前\(n\)项的和,
\((1)\)若\({a}_{m},15,{S}_{n} \)成等差数列,\(\lg {a}_{m},\lg 9,\lg {S}_{n} \)也成等差数列\((m,n\)为整数\()\),求\({a}_{m},{S}_{n} \)和\(m\),\(n\) 的值;
\((2)\)是否存在正整数\(m\),\(n\left(n\geqslant 2\right) \),使\(\lg \left({S}_{n-1}+m\right),\lg \left({S}_{n}+m\right),\lg \left({S}_{n+1}+m\right) \)成等差数列?若存在,求出\(m\),\(n\)的所有可能值;若不存在,试说明理由.